Embodiments of the invention relate to a non-invasive medical imaging technique, such as magnetic resonance elastography (“MRE”), used in radiology to measure stiffness of soft tissues.
Current MRE technology uses an acoustic driver system, developed by radiology researchers at Mayo Clinic. Current MRE technology, however, is limited to low frequency vibrations (e.g., 100 Hz or less) because it is based on pneumatic actuation. The wavelengths from the low frequency vibrations are smaller than the dimensions of the liver. Therefore, current pneumatic systems can be used to generate stable stiffness maps for the liver, which can be used to diagnose liver diseases, such as liver fibrosis. However, the wavelengths from the lower frequency vibrations are longer than the dimensions of other organs. As a result, current pneumatic systems generating low frequency vibrations cannot be used to generate stable stiffness maps for many organs such as the heart, prostate, pancreas, spleen, eye, etc. This is because the current inversion (a mathematical process to convert wave images to a stiffness map) strategies assume that the waves are propagating in a uniform infinite medium (i.e. the wavelengths are smaller compared to the dimensions of the organs of interest).